1. Field of the Invention
The present invention relates to a toner used for electrophotography, an electrostatic recording method, and a toner jet system recording method.
2. Description of the Related Art
In recent years, regarding an electrophotographic apparatus, it is considered that energy conservation is a large technical issue, and significant reduction in amount of heat required for a fixing apparatus has been studied. Consequently, regarding a toner, needs for so-called “low-temperature fixability” referring to that fixing can be effected at lower energy has grown.
As for the technique to make low temperature fixing possible, lowering of the glass transition temperature (Tg) of a binder resin in a toner is mentioned. However, lowering of Tg leads to degradation in thermal storage resistance of the toner. Therefore, it is usually difficult for this technique to ensure the compatibility between the low-temperature fixability and the thermal storage resistance of the toner.
In order to ensure the compatibility between the low-temperature fixability and the thermal storage resistance of the toner, a method in which a crystalline polyester is used as the binder resin has been studied.
In general, an amorphous resin used as the binder resin for the toner does not exhibit an endothermic peak in a measurement with a differential scanning calorimeter (DSC). However, in the case where a crystalline resin is contained in the binder resin, an endothermic peak appears in the DSC measurement. The peak temperature of this endothermic peak refers to the melting point of the crystalline resin.
The above-described crystalline polyester is a resin having a crystalline structure, does not have a clear Tg, and has a property of hardly softening at a temperature lower than the melting point. The melting point is the threshold of rapid melting accompanying sharp reduction in viscosity. Therefore, the crystalline polyester has been noted as a material having an excellent sharp melt property and ensuring the compatibility between the low-temperature fixability and the thermal storage resistance.
Japanese Patent Laid-Open No. 2002-318471 proposes a toner, wherein a crystalline polyester resin having a melting point of 80° C. or higher, and 140° C. or lower is used as a binder resin. However, regarding this technology, there is a problem in that fixing in a lower temperature range is not achieved because the crystalline polyester having a high melting point is used.
In order to solve the above-described issue, a technology has been proposed, in which a crystalline polyester having a lower melting point is used and a binder resin containing an amorphous substance is used (refer to Japanese Patent Laid-Open No. 2006-276074, for example). In the technology disclosed in Japanese Patent Laid-Open No. 2006-276074, a mixture of a crystalline polyester and a cycloolefin based copolymer resin is used as the binder resin. However, regarding this technology, the proportion of the amorphous substance is large, the fixability also depends on Tg of the amorphous substance and, thereby, there is a problem in that the sharp melt property of the crystalline polyester is not utilized sufficiently.
Then, technologies have been proposed, in which a crystalline polyester is contained as a primary component in a binder resin and it is aimed to make full use of the sharp melt property thereof (refer to Japanese Patent Laid-Open No. 2004-191927, Japanese Patent Laid-Open No. 2005-234046, and Japanese Patent Laid-Open No. 2006-084843, for example). However, according to the studies of the present inventors on the basis of the above-described disclosures, it was made clear that the melting point peak of the crystalline polyester in the toner became broad, and the sharp melt property of the crystalline polyester was not able to be utilized effectively. The reason therefor is believed to be that in the above-described technology, a toner was produced through a heating step at a temperature higher than or equal to the melting point of the crystalline polyester and, thereby, the crystallinity was degraded.
As described above, the compatibility between the low-temperature fixability and the thermal storage resistance of the toner still has a problem.